Polymer-based fiber composite materials are frequently used as construction material, since they have high mechanical strength combined with low weight. The matrix material typically consists of unsaturated polyester resins, vinyl ester resins or epoxy resins.
Fiber composite materials can be used, for example, in aircraft construction, in automobile construction or in rotor blades of wind power plants.
U.S. Pat. No. 5,973,099 A describes the production of compact polyurethanes with a thermolatent reactive resin mixture. The compact polyurethanes are preferably produced in an RTM method and, because of the use of polyols based on long-chain fatty acid derivatives, have low water absorption and therefore improved mechanical properties. A disadvantage is that the heat distortion resistance of the matrix is very low. In addition, the mold has to be primed prior to use with an external mold release agent for adequate demoldability. Moreover, the system has curing times of >10 minutes at a given processing temperature.
WO 2012163845 A1 describes the production of fiber composite components obtainable by impregnating fibers with a reactive resin mixture composed of polyisocyanates, dianhydrohexitols, polyols and optionally additives, and a process for production thereof. Preference is given here to using the vacuum assisted resin transfer molding (VARTM) and the resin transfer molding (RTM) methods. A disadvantage of the reactive resin mixtures is that they have a very long pot life at 35° C., and the viscosity rises only very gradually. Even at 80° C., curing of the reaction matrix over several hours is necessary.
DE 4416323 A describes heat-curable reactive resin mixtures comprising organic polyisocyanates, organic compounds having epoxy groups, and mixtures of particular tertiary amines (catalysts). The reactive resin mixtures are partly cured at temperatures up to 80° C. and fully cured at temperatures of 100 to 200° C. A disadvantage of these reactive resin mixtures is that they cure only at high temperatures and have long cycle times, which in turn leads to high energy and production costs.
The production of fiber composite materials by the preferred RTM method can in principle be divided into five stages: 1. mold preparation (for example polishing of the mold, application of the external mold release agent), 2. injection of the reactive resin into the mold, 3. curing of the reactive resin in the mold, 4. aftertreatment of the demolded fiber composite components by, for example, heat treatment, surface cleaning, etc., 5. painting, lamination or application of a decorative layer.
US 20040094859 A1 describes polyisocyanurate systems for production of fiber composite components by the pultrusion method. The polyisocyanurate systems described therein are equipped with internal mold release agent. In the pultrusion method, through the introduction of internal mold release agents, phase instability is exploited, in order that the pultrudates can be guided through the heated mold and do not stick therein. Because of this phase instability, it is not possible to use polyisocyanurate systems of this kind for the production of fiber composite components by the RTM method. Moreover, polyisocyanurate systems without subsequent heat treatment of the components at high temperatures have only a low NCO conversion of <90%.
In the case of the reactive resins used to date, the disadvantage is that every production of a fiber composite component has to be preceded by initial cleaning of the mold followed by priming again with an external mold release agent in a laborious manner. Specifically in the case of complex components, this is a costly step. Moreover, the reactive resins used to date have the disadvantage that it takes a long time until the reactive resin mixture has cured, which leads to low productivity. To increase the productivity, it is necessary to reduce the cycle time in the course of production. It is important here that the reactive resin mixture is mobile for long enough to completely impregnate the fibers, especially in the case of large moldings. On the other hand, the curing time should be very short, in order to reduce the cycle time. For economic reasons, a low curing temperature is desirable, since energy costs can be saved thereby.